The axial flux electric machine may be used for converting energy in numerous fields, such as the field of electrical power stations, in the form of alternators or servo-alternators, grouped together with a steam turbine or a gas turbine, or in the field of hydro power stations, in on-board systems, or indeed in applications concerning ship propulsion and other high-power engines.
Nevertheless, in its main application, such an electric machine constitutes an alternator for a wind turbine, and in particular an alternator having axial flux and permanent magnets.
Although not limited to this application, the remainder of the application describes in detail the advantages of the electric machine made in the form of an alternator with axial flux and permanent magnets as incorporated in a wind turbine.
Starting from this example, the person skilled in the art can readily deduce the adaptations needed to make an electric machine for use in other applications such as those mentioned above.
Over recent years, the trend has been to make wind turbines of very large diameter so as to obtain very high levels of electric power without excessively increasing the number of wind turbines.
The overall structure of wind turbines has followed this trend, and in particular the electric machines or alternators of such wind turbines are becoming ever more bulky.
This change in the size of alternators, and in particular of the rotors of alternators, leads to major constraints for manufacturers since, they need to adapt their production tooling to these changes in dimensions.
Furthermore, wind turbines of small dimensions continue to be sold, so manufacturers must conserve their entire range of production tooling so as to be capable of manufacturing a full range of elements needed for making electric machines of various dimensions.
At present, certain manufacturers of electric machines manufacture the rotors and the stators as single pieces, which gives rise to major constraints in terms of logistics when moving the electric machine to its site of use, and also to constraints during installation.
Furthermore, it appears that the techniques used for making the rotor and more particularly stators come up against a size limit, in particular concerning the secondary portion of the magnetic circuit in the stator.
Documents US 2007/001540 and US 2007/262674 are known that relate to an electric machine with axial flux. According to those documents, the electric machine comprises a rotor constituted by two disks secured to a rotary shaft, each disk having a magnetization zone constituting the primary portion of said machine. Those two disks are disposed on either side of the stator, with air gaps. In addition, the stator comprises a support mounted pivotally relative to the rotary shaft supporting the disks of the rotor, the support being secured to a plurality of active modules constituting the primary portion of the machine. That fastening is obtained by embedding the active modules in the material of said support which is obtained by molding. According to document US 2007/001540, such characteristics of the electric machine enable the time required for assembling the component elements of the stator to be reduced. According to document US 2007/262674, such characteristics of the electric machine seek in particular to combat a loss in efficiency of the machine due to a magnetic field that is too strong. Such a design of machine presents the drawback of requiring component elements to be assembled together directly in the factory, which implies the machine must be conveyed on site as a single unit, and consequently can constitute a major drawback for machines of large size. In addition, a malfunction of the stator requires the machine to be fully disassembled in order to replace the stator completely.
Document WO 2004/042891 A1 discloses an electric machine with axial flux and permanent magnets that presents a stator having a support and active modules constituting the secondary portion of the magnetic circuit, the active modules being fastened releasably and radially to the periphery of the support that is in the form of a wheel rim. In addition, the rotor comprises two disks surrounding the stator, i.e. they are disposed on either side of the stator, the inside faces of the disks having magnetization zones that constitute the primary portion of the magnetic circuit. The arrangement of the two disks on either side of the stator enables two axial air gaps to be established.